Download Arthropod Pest Management in Greenhouses and Interiorscapes E-1011

Arthropod Pest Management
in Greenhouses and Interiorscapes
E-1011
Oklahoma Cooperative Extension Service
Division of Agricultural Sciences
and Natural Resources
Oklahoma State University
Arthropod Pest Management
in Greenhouses and Interiorscapes
E-1011
Eric J. Rebek
Extension Entomologist/ Ornamentals and Turfgrass Specialist
Michael A. Schnelle
Extension Ornamentals/ Floriculture Specialist
Arthropod Pest Management
in Greenhouses and Interiorscapes
Insects and their relatives cause major plant
damage in commercial greenhouses and interiorscapes. Identification of key pests and an understanding of appropriate control measures are
essential to guard against costly crop losses. With
tightening regulations on conventional insecticides and increasing consumer sensitivity to their
use in public spaces, growers must seek effective
pest management alternatives to conventional
chemical control. Management strategies centered around the concept of integrated pest management (IPM) can provide growers powerful tools
for preventing pest problems before they occur or
at least mitigate their ornamental/economic consequences. This circular describes key arthropod
pests encountered in Oklahoma greenhouses and
interiorscapes and provides information on IPM
practices for their control. Specific pesticide recommendations are not provided but can be found
in Oklahoma Cooperative Extension publications
CR-6718, Management of Insects and Mites in
Greenhouse Floral Crops and E-832, OSU Extension Agents’ Handbook of Insect, Plant Disease,
and Weed Control. This circular replaces E-909,
Commercial Greenhouse Pests.
Aphids
Aphids feed on a wide range of greenhouse
crops. They are soft-bodied, pear-shaped insects
with somewhat long legs and antennae. There are
winged and wingless forms, varying from yellowgreen to red or brown, depending on species,
life stage, and reproductive stage. Regardless of
species, aphids are normally 1/8 inch or less in
length. Most have a pair of cornicles (structures
resembling tailpipes) protruding from the upper
surface of the rear end that can be seen easily us-
ing a hand lens.
Aphids feed on buds, leaves, stems, and roots
by inserting their long, straw-like, piercing-sucking mouthparts (stylets) and withdrawing plant
sap. Expanding leaves from damaged buds may be
curled or twisted and attacked leaves often display
chlorotic (yellow-white) speckles where cell contents have been removed. A secondary problem
arises from sugary honeydew excreted by aphids.
Leaves may appear shiny and become sticky from
this material, which supports the growth of black
sooty mold (a common greenhouse fungus).
Aphids are also notorious for their role as vectors of many viral diseases. However, of primary
concern in the greenhouse is their direct feeding
damage to plant tissues and overall reduction in
aesthetic quality of plants.
Aphids have great reproductive potential and
can achieve damaging numbers quickly. They typically give birth to female nymphs that can mature and begin reproducing in seven to ten days in
greenhouse conditions. Each aphid gives birth to
between 50 and 100 nymphs during a thirty-day
period, which can all occur in the absence of mating.
Winged females appear when overcrowding occurs or food supplies become depleted. When cold
weather is imminent, males and females appear
outdoors and mate. Eggs are laid on vegetation
and often overwinter successfully in Oklahoma.
Under greenhouse conditions, however, activity
is continuous and overwintering can occur in any
life stage.
The most common aphid in greenhouses is
the green peach aphid, Myzus persicae (Figure 1).
Adults are light to dark green, although pink or
orange individuals occasionally occur. Three very
faint lines are visible running down the upper sur-
Arthropod Pest Management in Greenhouses and Interiorscapes
1
Photo courtesy Scott Bauer, USDA Agricultural Research Service, www.insectiages.org
Virtually all greenhouse-grown crops are susceptible in varying degrees to aphids.
Photo courtesy Whitney Cranshaw, Colorado State
University, www.insectiages.org
Integrated Pest Management
Strategies
Figure 1. Green peach aphid adults, winged (top) and
wingless (bottom).
face of the body and a dark spot can be seen on
the abdomen. Using a hand lens, a distinguishing
feature can be observed: a small indentation is
present at the front and top of the head. Also, the
antennae are long enough to reach the cornicles,
and the base of each antenna bears an inwardly
projecting bump (tubercle) that is only visible
with a compound microscope. Green peach aphid
feeds on more than 100 plant species, including a
wide variety of vegetable and ornamental plants.
Key plants susceptible to aphids include: ageratum, alyssum, aster, celosia, chrysanthemum,
dahlia, gerbera daisy, Easter lilies, fuchsia, hydrangea, impatiens, monarda, pansy, pepper,
phlox, portulaca, primula, ranunculus, salvia,
snapdragon, tomato, verbena, viola, and zinnia.
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Cultural/Mechanical Control
and Monitoring
• Inspect all plants brought into the greenhouse from outdoors. Aphids can also enter
the greenhouse on clothing or through open
doors and vents.
• Weeds can harbor aphids, so control weeds
growing under benches and outside around
greenhouses to prevent recurring infestations.
• Monitor aphid populations in floral crops
weekly prior to flowering. Thorough plant
coverage with insecticides is more difficult to
achieve when flowers are present, and some
insecticides can be phytotoxic to flowers as
well as other plant parts.
• Place yellow sticky cards near doors and vents
to detect adult aphids. Inspect randomly selected plants for nymphs and wingless adults.
Be sure to examine lower leaf surfaces, stems,
and buds. Look for white, cast skins (molts)
and honeydew on upper leaf surfaces.
• In some cases, high aphid mortality can be
inflicted using a gentle stream of water to dislodge aphids from exposed plant surfaces.
Biological Control
• Natural enemies (predators and parasitoids)
are commercially available and can be released in the greenhouse. Predators include
ladybugs such as Adalia bipunctata, the predatory midge, Aphidoletes aphidimyza, and green
lacewings such as Chrysopa carnea. Parasitic
wasps include Aphelinus addominalis, Aphidius
colemani, and A. ervi.
Chemical Control
• Widespread resistance to insecticides has been
reported for many common aphid pests in the
greenhouse. However, several products with
novel modes of action are available that can
Arthropod Pest Management in Greenhouses and Interiorscapes
Fungus gnats, Bradysia spp. and Sciara spp.,
and shore flies, Scatella spp., were once considered minor nuisance pests in the greenhouse.
Production systems that employ misting equipment or are otherwise heavily irrigated create a
continuously wet soil environment favorable to
fungus gnat development. Plants grown in soil
rich in organic matter are also susceptible to fungus gnats. Damage is caused by the larvae, which
feed on organic matter and attack bulbs, roots,
and other fleshy plant parts. Larvae initially feed
on root hairs and eventually tunnel into the plant
stem. Delicate seedlings of many greenhouse species can be killed, with plants yellowing and often
wilting rapidly before death. Adult fungus gnats
and shore flies have been implicated in transmission of economically important plant pathogens
including the oomycete, Pythium, and the fungi, Verticillium, Botrytis, and Fusarium. Fungal
spores are typically carried from plant to plant on
the bodies of adult flies, but may also be present
in feces of fungus gnats. Fungus gnat larvae may
also transmit Pythium, Verticillium, Fusarium,
and Phoma.
Fungus gnats are delicate, dark gray to black
flies with long legs and antennae (Figure 2).
These insects reside on the soil surface and will fly
about when pots are disturbed or watering occurs.
Adults measure about 1/8 inch long and possess
one pair of transparent wings. Females lay clusters of 20 to 30 eggs on moist soil surfaces, par-
Photo courtesy Rick Grantham, Oklahoma State University
Fungus Gnats and
Shore Flies
Photo courtesy Whitney Cranshaw, Colorado State
University, www.insectiages.org
be rotated to manage aphids, while minimizing development of resistance. Many insecticides are harmful to natural enemies, so if a
biological control program is in place, choose
narrow-spectrum insecticides that minimize
negative effects on beneficial insects. For example, some products contain insect pathogens that specifically target the pest insect
but cause only minimal harm to non-target
organisms.
Figure 2. Darkwinged fungus gnat adult (top) and larvae (bottom).
ticularly soils high in organic matter. Adults live
for approximately ten days, but during that period
females may lay 250 to 300 eggs. Eggs hatch five
to six days after oviposition (egg laying). Larvae
are translucent, legless, 1/4 inch long white maggots with shiny black heads (Figure 2). They feed
for 10 to 14 days before pupating in the soil. After another five to six days, adults emerge from
their pupal cases, completing their life cycle within four weeks. Shore fly adults measure approximately 1/4
inch long, have black bodies, reddish eyes, and
gray wings that contain several clear spots (Figure 3). Though often mistaken for fungus gnats,
Arthropod Pest Management in Greenhouses and Interiorscapes
3
Photo courtesy Raymond Cloyd, Kansas State University
• To monitor adults, place yellow sticky traps
horizontally and directly above the soil surface
for maximum effectiveness. Fungus gnat larvae can be monitored by placing potato disks
or wedges on the soil surface; wedges should
be examined every two to three days for the
presence of larvae.
• Avoid excessive watering and keep soil slightly
dry, especially when trying to control infestations.
Figure 3. Shore fly adult caught on a yellow sticky
card. Note clear spots on wings.
shore flies have larger, more robust bodies and
relatively shorter legs and antennae. Eggs are laid
in areas of algal growth and larvae hatch within
four to six days following oviposition. There are
three larval stages; mature larvae measure about
1/4 inch long and are opaque, yellowish brown,
and lack a head capsule. The life cycle is complete in 15 to 20 days, depending on temperature. Larvae feed primarily on algae and are not
known to feed on plants, but adults deposit feces
on leaves, causing a reduction in aesthetic quality. Additionally, adult shore flies are known to
transmit black root rot and water-mold fungus in
their feces, especially under wet conditions.
Integrated Pest Management
Strategies
Cultural/Mechanical Control
and Monitoring
• Avoid accumulation of water, organic matter,
weeds, or debris on or under benches. Algal
growth should be controlled to manage shore
flies.
• Use pasteurized soil (start with clean soil and
do not store or stockpile soil outdoors or uncovered).
• Inspect new plant materials carefully, especially the roots. Look for larvae, particularly
in the upper inch of media in the container.
It is cheaper to rogue a few plants than to
control infestations later.
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Biological Control
• For fungus gnat control, use the predatory
mite, Hypoaspis miles, and the parasitic nematode, Steinernema feltiae. Nematodes are applied in water as a soil drench in pots or below
the bench. The rove beetle, Atheta coriaria, is
an effective predator of shore fly larvae.
Chemical Control
• Rotate insect growth regulators (IGR’s) with
other products to control fly pests. IGR’s interfere with development and growth of immature fungus gnats and shore flies. Also,
use formulations of Bacillus thuringiensis var.
israelensis (Bti).
Scale Insects and
Mealybugs
Greenhouse plants can serve as hosts to a wide
variety of scale insects. These pests are closely related to aphids and are highly variable in shape,
color, and size, although most species are less than
1/4 inch long. Scales feed by inserting their long,
needle-like mouthparts into plant tissue and extracting plant sap, resulting in reduced plant vigor, stunted growth, reduced photosynthesis, and
dieback. Scales are highly specialized insects that
most people misdiagnose as abnormal growths or
disease symptoms due to their concealment within
hardened bodies or beneath dome-like, waxy covers. Common greenhouse species in Oklahoma
include black scale, Saissetia oleae, hemispherical
scale, Saissetia coffeae, and brown soft scale, Coc-
Arthropod Pest Management in Greenhouses and Interiorscapes
Photo courtesy United States National Collection of Scale
Insects Photographs Archive, USDA-ARS, www.insectimges.org
Photo courtesy Sonya Broughton, Dept. of Agriculture & Food, Western Australia, www.insectimages.
org
Photo courtesy United States National Collection of Scale Insects Photographs Archive,
USDA-ARS, www.insectimges.org
Figure 4. Black scale (upper left), hemispherical scale
(upper right), and soft brown scale (lower left).
cus hhesperidum (Figure 4). These species belong
to a family of scales called soft scales (Coccidae).
Like aphids, soft scales excrete honeydew, which
can accumulate on upper leaf surfaces and support the growth of black sooty mold. Other scale
pests in the greenhouse include armored scales
(Diaspididae) and pit scales (Asterolecaniidae).
While feeding, adults inject toxic saliva into
the host plant, causing cellular damage within affected tissues. Adult females are sac-like, wingless,
and typically legless. Adult males have legs and
one pair of wings, but lack mouthparts and, thus,
do not feed. As such, upon emergence they seek
out and mate with available females, then die. In
some species, males are rare or entirely lacking,
and virgin females produce clones of themselves.
Live young or eggs are produced under the female’s body or waxy cover. First stage nymphs are
called crawlers because they have legs and move
about for one or two days in search of prime feeding areas on the plant. Crawlers then insert their
mouthparts into plant tissue and settle, forming
their waxy cover as they feed. Most species are
immobile for the remainder of their lives. Settled
crawlers develop through several molts, losing
their legs during the first molt. One to eight generations can occur within a year, depending on
species and temperature.
Mealybugs (Pseudococcidae) are soft-bodied insects that measure about 1/8 to 1/4 inch in length.
All mealybugs are covered by a white granular or
cottony layer of wax. Many species possess long,
waxy filaments or shorter tufts projecting outward
from the body. The life cycle of most species is
similar with females laying 300 to 600 eggs in
cottony sacs usually located beneath the female.
Following oviposition, eggs hatch in seven to ten
days into tiny yellowish nymphs (crawlers). The
long-tailed mealybug is slightly different because
females give birth to living young. Mealybugs injure plants by sucking sap from tender foliage,
flowers, stems, fruits, and roots. Heavy infestations result in stunted and distorted new growth.
Like soft scales, mealybugs excrete honeydew,
which can give rise to black sooty mold. Depending on species and temperature, the complete life
cycle can take six weeks to two months, though
mealybugs can be found in the greenhouse year
round.
Many species occur on greenhouse floral
crops, but perhaps the most common is the cit-
Arthropod Pest Management in Greenhouses and Interiorscapes
5
Photo courtesy Sonya Broughton, Dept. of Agriculture & Food, Western Australia, www.insectimages.org
• Examine new plant material carefully for the
presence of scales and mealybugs on stems
and leaves.
• Pheromone traps can be used to capture male
citrus mealybugs for monitoring the presence
of mealybugs in greenhouses.
Biological Control
• Soft scales are controlled with parasitic wasps
released into the greenhouse. Many wasp species specialize on one or several scale insects,
so be sure to properly match the biological
control agent with its scale host. For instance,
Metaphycus luteola is very effective at controlling brown soft scale, but M. helvolus is better
suited to controlling hemispherical scale.
• Various parasitic wasps for controlling mealybugs are available commercially. Citrus mealybug is effectively controlled using Leptomastix
dactylopii in conjunction with the ladybug
predator, Cryptolaemus montrouzieri, known
as mealybug destroyer.
rus mealybug, Planococcus citri (Figure 5). Citrus mealybugs have a white, powdery substance
covering their bodies and white, waxy filaments
projecting from the end of their abdomen. They
also have shorter filaments of wax along the body
margins and a faint, gray stripe running down the
length of their body. This pest feeds on more than
27 families of host plants, including amaryllis,
begonia, coleus, cyclamen, and dahlia.
Chemical Control
• Most scale species, especially soft scales, and
mealybugs are effectively controlled with systemic insecticides. Armored scales can be
controlled or at least suppressed with certain
systemic insecticides, but horticultural oil
can be used very effectively against armored
scales.
• Commercially available insecticidal soaps are
also an effective option.
• Minor mealybug infestations are often controlled with a 50/50 mixture of common rubbing alcohol and water.
Integrated Pest Management
Strategies
Whiteflies
Figure 5. Adult citrus mealybugs on Kalanchoe, Kalanchoe spp.
Cultural/Mechanical Control
and Monitoring
• Monitor for scales and mealybugs by closely
examining stems and both sides (especially
undersides) of leaves at least once per week.
Look for deposits of honeydew and black
sooty mold on upper leaf surfaces.
6
Whiteflies are not true flies, but are close relatives of aphids and scales. They measure 1/16
inch long, have four wings, and are orange underneath. They resemble small white moths due
to the white, waxy powder on top of their bodies
(Figure 6). Whiteflies reside on the underside of
leaves and will fly readily when disturbed. During
Arthropod Pest Management in Greenhouses and Interiorscapes
Photo courtesy W. Billen, Pflanzenbeschaustelle, Weilam
Rein, www.insectimages.org
Figure 6. Adult and larvae of greenhouse whitefly.
heavy infestations, a “white cloud” appears during
watering or when plants are disturbed. These insects feed through piercing-sucking mouthparts,
sometimes causing stippling (small, discolored
spots) on leaves. Plants eventually lose vigor as
essential nutrients are withdrawn with the plant
sap. Like their close relatives, whiteflies excrete
honeydew, supporting the growth of black sooty
mold on plant surfaces. Whiteflies are problematic for several reasons: they have high reproductive
rates, rapidly develop resistance to insecticides,
some can transmit plant viruses, and they attack
a wide range of major ornamental crops. Poinsettia, chrysanthemum, fuchsia, many bedding
plants, and tomatoes are particularly susceptible
to whiteflies.
Despite the fact that they are tropical insects,
whiteflies are found in greenhouses year round.
They spread from greenhouse to greenhouse via
transport of host plants and by attaching to workers’ clothing. Yellow clothing should not be worn
by workers as this color is particularly alluring to
whiteflies. Several species are of economic importance to greenhouse production, including greenhouse whitefly, Trialeurodes vaporariorum, sweetpotato whitefly, Bemisia tabaci biotype B (also
known as silverleaf whitefly, Bemisia argentifolii),
and sweetpotato whitefly, Bemisia tabaci biotype
Q. Biotypes B and Q of sweetpotato whitefly cannot be distinguished based on physical traits, so
only DNA tests can confirm their true identity.
It is important to make the correct determination
because biotype Q is resistant to several classes
of insecticides. Contact your county Extension
office to inquire about how to determine the predominant biotype present in your greenhouse.
Female whiteflies usually deposit eggs in a
circular pattern and most frequently on the underside of younger, upper foliage. Adult females
may lay as many as 150 to 250 eggs in their lifetime. Eggs are tiny, spindle shaped, and attached
to the leaf surface by a thin stalk. Eggs appear
creamy when laid but eventually darken. Newly
hatched nymphs emerge from the eggs in five to
ten days and seek feeding sites. After inserting
their mouthparts into leaf tissue, they remain stationary for three weeks, during which three molts
occur. All nymphal stages are flat, transparent
to yellow-green, and appear scale-like. At the
end of this period, the whitefly transforms into a
non-feeding, yellowish-green “pseudopupa” with
two conspicuous eyes. About one week later, the
winged adult emerges and begins laying eggs within a week. The entire life cycle is complete within
four to five weeks, depending on temperature.
Sweetpotato whitefly holds its wings closer
to the body and appears smaller than greenhouse
whitefly. Damage is similar to that of greenhouse
whitefly, but sweetpotato whitefly can reproduce
more aggressively, particularly because insecticide
resistance is acquired rapidly with this species.
Poinsettias are extremely susceptible to sweetpotato whitefly. Because whitefly populations can
increase quickly, it is essential to monitor their
populations early in the production schedule.
Early vigilance in poinsettia crops is also important, because plants are susceptible to pesticide
damage once they begin showing color.
Integrated Pest Management
Strategies
Cultural/Mechanical Control
and Monitoring
• Monitor for sessile stages of whitefly and their
eggs by closely examining undersides of leaves,
especially early in the production cycle. Look
for deposits of honeydew and black sooty mold
on upper leaf surfaces.
Arthropod Pest Management in Greenhouses and Interiorscapes
7
Biological Control
• Several parasitic wasps are commercially available for whitefly control. Encarsia formosa attacks greenhouse whitefly larvae and Eretmocerus eremicus parasitizes both greenhouse,and
silverleaf (current name for sweetpotato)
whitefly. Eretmocerus mundus specifically
controls silverleaf whitefly and can survive
under a variety of climatic conditions. This
wasp can be introduced into the greenhouse at
any time, including early in the season. The
predatory mite, Amblyseius swirskii, feeds on
whitefly eggs and larvae as well as thrips. This
predator performs best when both prey items
are available. Delphastus catalinae, a small
black lady beetle, is also commercially obtainable.
Chemical Control
• Systemic and some contact insecticides have
provided effective control of whiteflies, but
be sure to rotate among chemical classes to
prevent the development of resistance. Contact insecticides should be directed at the underside of leaves and applied when first- and
second-instar whitefly larvae are present.
Thrips
Most thrips species measure no more than 1/8
inch long, have slender bodies, and have two pairs
of stalk-like wings fringed with long hairs (Figure
7). Populations often proliferate on weeds growing around greenhouses during summer months
and may be carried in by air currents through
open vents or doors (especially during wheat harvest in Oklahoma). Thrips attack a wide range of
crops and can be found in buds, on flower petals,
and in axils of leaves. While adults can be seen
without a hand lens, they usually hide in buds or
flowers. Thrips can be detected by thorough visual
inspection of plants and by tapping foliage, buds,
8
Photo courtesy Alton N.Sparks, Jr., University of Georgia, www.insectimages.org
• Weeds can be an important source of whiteflies, so control weeds growing under benches
to prevent recurring whitefly problems.
Figure 7. Onion thrips (left) and western flower thrips
(right).
or flowers over white paper. Adults can be yellow,
brown, tan, or black, depending on species.
Using their saw-like ovipositor, adult females
lay their eggs in leaves and other plant tissue. In
two to eight days, eggs hatch, and larvae immediately begin to feed. After feeding for ten to fourteen days, larvae burrow into the soil and pupate.
Adults emerge about four days later. The life
cycle is complete in as little as two weeks, though
cooler temperatures may delay completion of the
life cycle up to a month.
Thrips have rasping mouthparts that scrape
tender leaves and petals, creating a wound allowing them to suck exuding plant sap. Thrips injury
appears as white or silver streaks on affected plant
parts, which turn tan or brown as cells die. In addition, thrips feeding on newly expanding leaves
can distort tissue severely, resulting in cupping
(curled leaf margins) or irregularly shaped leaves,
buds, and flowers. A sign of an infestation is the
presence of green to black fecal droppings on
leaves and petals.
Arthropod Pest Management in Greenhouses and Interiorscapes
Adults and larvae transmit two important
tospoviruses, tomato spotted wilt virus (TSWV)
and impatiens necrotic spot virus (INSV). The
predominant vector of these important plant
diseases is western flower thrips, Frankliniella occidentalis. Male western flower thrips are pale yellow and have a narrow abdomen; whereas females
are larger, yellow to dark brown, and have a more
rounded abdomen. Each female may live up to six
weeks, and may produce 150 to 250 eggs during
her lifetime. Larvae develop through two instars
and are yellow.
Thrips attack at least 300 species of plants.
New Guinea impatiens, chrysanthemums, and
gloxinias are especially susceptible to tospoviruses, and symptoms vary with host plant from
bulls-eye patterns on foliage to brown sap oozing from lesions on stems. Plants infected with
TSWV or INSV must be destroyed because the
diseases are incurable. Therefore, controlling
thrips is important in preventing transmission of
these economically important diseases as well as
reduced aesthetic quality due to feeding. Plants
showing symptoms of disease can be submitted
to the Plant Disease and Insect Diagnostic Lab
at Oklahoma State University for evaluation.
Instructions for preparation and submission of
samples can be found at http://www.ento.okstate.
edu/pddl/.
Integrated Pest Management
Strategies
Cultural/Mechanical Control
and Monitoring
• Know your source of plants. Do not introduce new plants that may have the virus into a
greenhouse containing healthy plants. Thrips
can quickly spread the virus to epidemic levels.
• Eliminate sources of thrips by removing weeds
growing under benches and outside around
greenhouses.
• Exclude thrips from the greenhouse by installing vent/fan screens and double doors.
• Monitor for adult thrips with blue or yellow
sticky cards placed just above the plant can-
opy and check cards at least once per week.
If adults are detected, closely examine plants
around the sticky card for thrips and plant
damage.
• Thrips can also be detected by tapping foliage,
buds, or flowers over white paper.
Biological Control
• Predatory mites such as Hypoaspis miles,
Amblyseius cucumeris, and A. swirskii, and
the minute pirate bug, Orius insidiosus, are
commercially available for release against
thrips. Amblyseius mites should be released
before thrips populations build up to damaging levels. The soil-inhabiting mite, Hypoaspis miles, is available for release against thrips
pupae, root-infesting aphids, and fungus gnat
larvae. The parasitic nematode, Steinernema
feltiae, is applied in water as a soil drench to
control thrips pupae.
Chemical Control
• Thrips are normally controlled with contact
insecticides, but acceptable levels of control
are often difficult to achieve because thrips
inhabiting flowers are often well protected
from sprays. Systemic insecticides will not
work against thrips feeding on flower buds or
petals because the active ingredients cannot
be transported to those tissues.
• If a biological control program is in place,
choose selective insecticides such as IGR’s or
products containing the insect-killing fungus,
Beauveria bassiana, to minimize harmful effects on natural enemies, especially predatory
mites.
Mites
Mites are arachnids, not insects, and thus
are more closely related to scorpions and spiders.
Unlike insects, adult mites have four pairs of legs
regardless of the species. However, immature
mites can have three pairs of legs early in their
life cycle, so be careful when trying to diagnose a
pest problem.
Arthropod Pest Management in Greenhouses and Interiorscapes
9
Photo courtesy Eric Coombs, Oregon Department of Agriculture, www.insectimages.org
Photo courtesy David Cappaert, Michigan State University, www.
insectimages.org
Probably the most common mite in the
greenhouse is the two-spotted spider mite, Tetranychus urticae. This mite measures about 1/50
inch long, requiring at least a 10X hand lens to
aid in its identification. Two-spotted spider mites
may be yellow or green with two, and occasionally
four, dark spots on their bodies (Figure 8). This
mite feeds by piercing leaf tissue with its thin,
whip-like mouthparts and sucking the plant sap
exuded at the wound site. Feeding causes chlorotic stippling of leaves, giving the appearance of
fine, yellowish to white speckling on the foliage.
Stippling is distinctive and is readily recognized
by experienced growers. Spider mites are most
likely to be found on the underside of leaves and
in the flowers. As populations increase, spider
mites often spin webbing over foliage and flowers
(Figure 8).
Duration of the life cycle varies greatly with
temperature in the greenhouse. But under hot,
Integrated Pest Management
Strategies
Figure 8. Adult two-spotted spider mites (top) and
webbing produced by gorse spider mite (bottom).
10
dry conditions, it may take as little as seven days
for mites to develop from egg to adult. At 70°F
the life cycle is twenty days but only half that when
temperatures are at 80°F. High temperatures and
low relative humidity favor mite development. In
two to five days, eggs hatch into six-legged larvae that feed for a short time. Larvae then develop into eight-legged nymphs that pass through
two stages, the protonymph and deutonymph.
Between each stage, larvae and nymphs enter an
inactive resting stage that lasts a short time. The
eight-legged adult finally emerges from the last
resting stage. Because each female may deposit
100 eggs or more during her lifetime, there is a
high potential for rapid population growth.
Cyclamen mites, Phytonemus pallidus, are
only 1/100 inch long at maturity. These mites
cannot be seen without high magnification and
are translucent with a brownish tinge. Cyclamen
mites attack a wide range of plants, feeding on
buds and adjacent immature leaves. They attack growing points of plant tissue, which causes
twisting and stunting of affected tissue, and new
growth may appear purplish. Damaged leaflets
curl from outside inward because feeding causes
small depressions to form in young leaves. Damaged flower buds may grow into distorted flowers
or may not open at all.
High humidity (80 percent or more) with a
cool temperature (60°F or less) favors their development. The life cycle from egg to adult can
occur in only two weeks, with the female living
up to four weeks and laying up to 100 eggs in her
lifetime.
Cultural/Mechanical Control
and Monitoring
• Monitor for mites by examining plants closely
for stippling, webbing, and/or herbicide-like
damage. Be especially vigilant when ambient
conditions are conducive to the development
of spider mites (hot and dry) and cyclamen
mites (cool and wet).
Arthropod Pest Management in Greenhouses and Interiorscapes
Biological Control
• Amblyseius californicus, Phytoseiulus persimilis, and Neoseiulus fallacis are predatory mites
that can be used to control two-spotted spider
mites. A predatory midge, Feltiella acarisuga,
is also available for spider mite control. While
relatively new, a small lady beetle, Stethorus
punctillum, is now available and has the advantage of flying to its prey.
Chemical Control
• Several miticides are available for mite control, but be sure to check which life stages are
controlled by each product. Resting stages
tend to be more tolerant of miticides, but
some newer products can kill eggs as well as
other life stages.
• Repeated applications of contact insecticides
may be necessary when mites are abundant.
However, care must be taken in choosing a
product when biological control programs are
in place.
• During hot Oklahoma summers, it may be
necessary to schedule pesticide applications as
often as two days apart or to be as aggressive
as the label permits.
• Cyclamen mites can be killed by immersing
infested plant material in hot water (110°F)
for fifteen minutes. Different plants should
be tested for sensitivity to hot water before
attempting this treatment.
Leaf Miners
A variety of insects mine leaves in nature, but
several species from a family of flies (Agromyzidae)
are the primary leaf miner pests in greenhouses.
Adult leaf miners are stocky flies that measure
about 1/12 inch long (Figure 9). Using their ovipositor, females puncture the leaf surface and insert tiny eggs within the leaf. Each female can lay
up to 100 eggs in her two- to three-week life span.
These puncture wounds turn white shortly after
oviposition, giving the leaf a speckled appearance
following multiple attacks. In five to seven days,
eggs hatch into white maggots that grow to 1/10
inch long at maturity. Larvae tunnel within leaves
for about two weeks, then become pupae. Depending on species, pupation takes place in or on the
soil, in leaf mines, or on leaf surfaces. About two
weeks later, the adult fly emerges from the pupa,
repeating the life cycle. Leaf miners can survive
transport of cuttings in the egg, larval, or pupal
stage, so infestations may result from shipment
of infested material.
Tunneling maggots feed just under the outer cell layer of leaves, causing unsightly runs or
mines as they feed. Damage causes reduced aesthetic quality, but tunneling usually does not kill
the plant. Problematic greenhouse species include the serpentine leaf miner, Liriomyza trifolii,
and the chrysanthemum leaf miner, Phytomyza
atricornis. Adult serpentine leaf miners have a
black body with yellow markings, a yellow head,
and brown eyes. As its name suggests, mines created by this species are serpentine in appearance.
Adult chrysanthemum leaf miners are larger and
grey to black with many hairs on their body.
Their mines can appear blotchy as well as serpentine and tend to be found near the leaf mid-vein.
Photo courtesy Central Science Laboratory, Harpenden Archive, British Crown, www.insectimages.org
• Like thrips, spider mites can be detected by
careful visual inspection and by tapping foliage, buds, or flowers over white paper.
• Highly susceptible plants can be used as indicator plants to a developing cyclamen mite
problem. For example, African violets will not
bloom, followed by the development of hairy,
stunted leaves. Impatiens and petunias will
exhibit distorted terminal growth.
Figure 9. Adult chrysanthemum leaf miner.
Arthropod Pest Management in Greenhouses and Interiorscapes
11
Cultural/Mechanical Control
and Monitoring
• Regularly monitor susceptible plants, including aster, chrysanthemum, dahlia, and gerbera daisy. Remove mined leaves before adult
flies emerge and be sure to destroy infested
foliage.
Biological Control
• Three parasitic wasps, Dacnusa sibirica, Opius
pallipes, and Diglyphus isaea, have been used
successfully for leaf miner control.
Chemical Control
• Serpentine leaf miner is highly resistant to
organophosphate, carbamate, and pyrethroid
insecticides. In general, some systemic insecticides and IGR’s can effectively control leaf
miners.
Caterpillars
Larvae of several species of moths (caterpillars) can attack greenhouse crops. Caterpillars
vary in appearance, but all have chewing mouthparts, three pairs of segmented “true” legs on the
first three body segments behind the head, and
five or fewer pairs of fleshy, unsegmented, abdominal prolegs (Figure 10). These prolegs have
tiny hook-like structures called crochets at the
tips that allow the caterpillar to grip stems, petioles, and foliage.
Feeding damage occurs on leaves when the
caterpillar chews holes or “skeletonizes” leaf tissue (feeding only on tissue between veins). A severe infestation of caterpillars can quickly defoliate entire plants. Injury may not be noticed when
caterpillars are young, but damage becomes increasingly evident as these pests develop and grow.
Caterpillars are particularly troublesome during
the summer months when moths are active outdoors. Most moths are nocturnal and attracted
to lights, entering a greenhouse through open
12
Photo courtesy Frank Peairs, Colorado State University,
www.insectimages.org
Integrated Pest Management
Strategies
Figure 10. Beet armyworm caterpillar. Note the three
pairs of true legs near the head and five pairs of fleshy,
abdominal prolegs.
doors or vents. Mated female moths then proceed
to lay eggs on greenhouse crops. Beet armyworm,
corn earworm, European corn borer, and various
cutworms, leaf tiers, and leaf rollers are a few of
many caterpillars that can occasionally damage
tender plants.
Control is similar for most caterpillar pests,
with stomach poisons being commonly used.
Control with Bacillus thuringiensis is often effective, but efficacy is greatest against young caterpillars. Repeat applications of this bacterium are
necessary to keep new growth surfaces covered as
plants grow. If caterpillars enter stems or buds,
they become very difficult to control.
Integrated Pest Management
Tactics
Cultural/Mechanical Control
and Monitoring
• Exclude moths by installing vent screens and
keeping doors closed at night.
• Regularly monitor plants for symptoms of
feeding damage and signs of caterpillars such
as egg masses, cast skins, frass (solid waste),
or the insects themselves.
• Remove and destroy any caterpillars or foliage
containing egg masses.
Biological Control
• Parasitic wasps in the genus Trichogramma are
commercially available and will attack moth
egg masses.
Arthropod Pest Management in Greenhouses and Interiorscapes
Integrated Pest Management
Tactics
Chemical Control
• Reduced-risk “biopesticides” contain insectkilling pathogens that can be highly effective
against caterpillar pests and are safe for greenhouse workers and natural enemies. Choose
insecticides containing the bacterium, Bacillus thuringiensis (Bt) var. kurstaki, the fungus,
Beauveria bassiana, or the active ingredient,
spinosad. These products are most effective
against young caterpillars. Other insecticides can be used to control older larvae and
adults.
Sanitation and soil pasteurization are most
helpful in preventing or controlling springtails.
The predatory mite, Hypoaspis miles, will feed on
springtails as well as other soil-dwelling pests.
Slugs and Snails
Slugs and snails are mollusks rather than
insects and are related to clams and oysters.
Whereas snails have a hard shell, slugs lack a shell
(Figure 12). Both vary greatly in size, ranging
from one-half to four inches in length. Clusters
of 20 to 100 eggs are laid by slugs or snails in
moist crevices in the soil or in containers. Eggs
hatch in ten days or less, with maturity occurring within three months to one year. Using their
rasping mouthparts, slugs and snails feed at night
on tender seedlings and leaves. Feeding damage
appears as irregularly shaped holes with smooth
edges, and may be confused with injury caused
by caterpillars. Seedling plants can be completely
consumed. During the day, slugs and snails hide
beneath pots, benches, plant debris, or other
concealed locations. Both prefer moist areas, so
greenhouses can be ideal environments for their
growth and development. Slugs and snails exude
a slippery liquid from a muscular “foot” as they
travel. When this substance dries, a shiny track
is left behind. Besides feeding damage, this track
is usually the best way to detect the presence of
these pests.
Springtails
Photo courtesy Susan Ellis, www.insectimages.org
Photo courtesy Joseph Berger, www.insectimages.org
Springtails are very small, white, gray, black,
brown, or purple insects that lack wings (Figure
11). A specialized structure beneath the tip of
the abdomen enables them to jump an inch or
more into the air. Springtails prefer dark, damp
areas high in organic matter. They feed primarily
on fungi, algae, and decaying organic matter in
growing media. However, feeding may occur on
tender roots of some crops. Damage may occur
to seedlings, but springtails rarely cause enough
harm to be considered major pests. When large
populations occur, they are easily found on the
soil surface or can be seen “springing” about during watering or moving a crop. Springtails may be
spread in unpasteurized potting soil, transported
on clothing, via plant contact, or simply migrating indoors from nearby habitats.
Figure 11. Springtail.
Figure 11. Gray garden slug.
Arthropod Pest Management in Greenhouses and Interiorscapes
13
Integrated Pest Management
Tactics
Cultural/Mechanical Control
and Monitoring
• Practice good sanitation and keep problematic areas as dry as possible.
• Inspect incoming plants and pots for slugs
and snails.
• Eliminate sources of slugs and snails by removing weeds growing both inside and outside around greenhouses.
• Slugs avoid copper, so wrap copper tape
around bench legs or install copper flashing
around raised beds.
Biological Control
• No predators or parasites are commercially
available in the U.S., although research is
ongoing in this area.
Chemical Control
• Chemical baits are commercially available for
slug control. Baits are usually formulated in
bran and must be eaten by slugs to be effective. Place baits in the evening when slugs are
most active and irrigate prior to bait placement to draw out slugs, leading to more frequent contact with the bait.
• Rotate among active ingredients to counter
avoidance and resistance to baits.
General IPM Practices
for Greenhouses and Interiorscapes
1. Establish and maintain a thorough recordkeeping system for all pest management
practices.
2. Become familiar with each crop’s potential
pest problems.
3. Conduct a pre-crop inspection of production areas for potential pest problems.
4. Always inspect incoming plants for pests
immediately upon arrival. Reject the shipment rather than treating or accepting
“slight” infestations.
14
5. Inspect crops for signs and symptoms of
pests on a regular basis.
6. Choose appropriate control methods carefully and know when to apply them.
7. Discard and destroy severely infested plants.
8. Physically exclude or confine pests.
9. Always pasteurize media that has soil as a
component.
10. Consider using biological controls whenever
possible.
Arthropod Pest Management in Greenhouses and Interiorscapes
Oklahoma Pest Control Supply Companies
American Plant Products and Services, Inc.
9200 Northwest 10th Street
Oklahoma City, OK 73127
405-787-4833
www.americanplant.com
Other Companies Outside Oklahoma:
Winfield Solutions regional locations/offices:
www.winfield.com
1819 NW 5th St
Oklahoma City, OK 73106
405-232-2493
BioWorks
100 Rawson Road
Suite 205
Victor, NY 14564
800-877-9443
www.bioworksinc.com
11391 East Tecumseh St.
Tulsa, OK 74116
918-234-0560
IPM Laboratories, Inc.
Locke, NY
315-497-2063
www.ipmlabs.com
801 North 54th St.
Enid, OK 73701
580-234-8004
Hydro-Gardens
8765 Vollmer Rd
Colorado Springs, CO 80908
888-693-0578
www.hydro-gardens.com
Alpha Scents, Inc.
1089 Willamette Falls Drive
West Linn, OR 97068
503-342-8611
www.alphascents.com
Trécé, Inc.
7569 Highway 28 West
Adair, OK 74330
918-785-3061
www.trece.com
Reference:
Gill, S., R.A. Cloyd, J.R. Baker, D.L. Clement, and
E. Dutky. 2006. Pests & Diseases of Herbaceous
Perennials: The Biological Approach. Ball Publishing Co., Batavia, IL.
Oklahoma State University, in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans
with Disabilities Act of 1990, and other federal laws and regulations, does not discriminate on the basis of race, color, national origin, gender, age, religion, disability, or status as a veteran
in any of its policies, practices or procedures. This includes but is not limited to admissions, employment, financial aid, and educational services.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, the Director of Oklahoma Cooperative
Extension Service, Oklahoma State University, Stillwater, Oklahoma. This publication is printed and issued by Oklahoma State University as authorized by the Vice President, Dean, and
Director of the Division of Agricultural Sciences and Natural Resources and has been prepared and distributed at a cost of $9.12 per copy. Revised 1113 GH.
Arthropod Pest Management in Greenhouses and Interiorscapes
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